The invention relates to a layer that contains an organic, transparent, electrically conductive material, a method for producing such a layer, and the use of said layer, in particular in LC displays.
Conventional LC displays have two glass substrates that are coated on one side with a polarization filter and on the other side with a structured electrode (one of the electrodes can also be unstructured) made of indium tin oxide (ITO), which is coated with an orientation layer, for example made of polyimide. The orientation layer is used to induce a privileged direction of molecules, for example, parallel to one surface. The orientation is usually produced by means of friction. With the orientation layers, the coated glass substrates define the opposite surfaces of a liquid crystal. ITO is deposited by means of sputtering in a vacuum process, which is expensive. This is followed by the structuring of the ITO layer by means of photolithography, in which the exposed ITO is etched away by means of HBr or HCl and HNO3. The above-mentioned materials and process steps make the production of the layer structure expensive and time-consuming.
Among other things, the European patent applications 0440975 and 0686662 have disclosed organic, electrically conductive polythiophene derivatives; the latter application mentions, among other things, using polyethylene dioxythiophenes as electrode material for LC displays. The polythiophenes are produced by thiophenes being oxidatively polymerized, particularly in the presence of polyacids. During the polymerization, the polythiophenes are given positive charges. The polymer produced is deposited onto the glass substrate and is converted into the layer by drying and optional tempering. This production is simpler and less expensive than the production of ITO layers. The structuring of the organic, conductive polymers is somewhat less expensive than that of ITO because no strong anorganic acids have to be used for the etching. The method for producing the entire layer structure of LC displays, however, remains quite expensive.
The object of the invention is to disclose a structure, which performs the functions of a structured, organic, electrically conductive, transparent electrode and an orientation layer, a cost-reducing and time-saving method for producing such a structure, and uses of this structure.
This object is attained with a layer of the type mentioned at the beginning, which is characterized in that the layer is oriented by means of a method of the type mentioned at the beginning, in which layers produced in a conventional manner are oriented, which contain an organic, electrically conductive, transparent material, and is attained with the use of the layer in an LC display as a combined electrode and orientation layer. The layer according to the invention thus renders an additional orientation layer superfluous. As a result, the method for producing LC displays can be executed in a manner that saves a significant amount of time and expense without becoming more complex, because its execution only makes use of conventional process steps and devices. The layer according to the invention is particularly used in LC displays in which it replaces the previously conventional structure made up of an electrically conductive, transparent electrode and an orientation layer. The structure according to the invention is thus embodied more simply than known structures and can be produced with fewer process steps and the materials are cheaper and more environmentally friendly.
It is advantageous if the material is a doped polymer, which is preferably a mixture of a polymer, which is selected from the group including polythiophenes, polyacetylenes, polypyrroles, polyanilines, and the like, at least one polyanion, which is preferably comprised of organic compounds containing di- and polyhydroxy- and/or carboxylic acid- or sulfonic acid groups, and particularly preferably at least one polyanion comprised of polycarboxylic acids or polysulfonic acids. In this connection, a xe2x80x9cdopedxe2x80x9d polymer is understood to be a polymer which has been modified by means of oxidation or reduction reactions to form a batch-transfer complex with a metallic, electrical conductivity characteristic.
It is advantageous if the conductive polymer was produced by means of photo-induced or electron beam polymerization or if the conductive polymer was modified in such a way that it became photo-cross-linkable, and was then photopolymerized (in the following, the terms xe2x80x9cphotopolymerizationxe2x80x9d and xe2x80x9cphoto-cross-linkingxe2x80x9d will always be used for both photopolymerization and electron beam polymerization as well as for both photo-cross-linking and electron beam cross-linking). With polymers of this kind, the method can be simplified particularly if the layer, for example for use in an LC display, must be photolithographically structured by means of selective etching, because the production of a photoresistive masking can then be eliminated.
Such a simplification can also be achieved if the layer containsxe2x80x94optionally in addition to the photopolymerized or photo-cross-linked conductive polymerxe2x80x94a bonding agent that is a polymer, which has been cross-linked by irradiation. This multitude of possibilities permits flexible adaptation to other requirements of the method.
It is favorable if the photopolymerizable starting material for the polymer, the cross-linkable polymer, and/or the cross-linkable bonding agent can also be photo-oriented because in the irradiation for the polymerization or cross-linking, when linearly polarized light is used, for example by virtue of the illumination being routed through the polarization filter of the LC display, the orientation of the layer or at least the induction of the privileged direction or the setting of the tilt angle can be executed at the same time.
However, the orientation can also be advantageously producedxe2x80x94as in conventional orientation layersxe2x80x94by means of friction, because it has surprisingly been determined that this orientation method also functions with electrode layers comprised of organic, electrically conductive materials.
Other advantageous embodiments of the layer according to the invention and the method according to the invention ensue from the dependent claims.